Method and system for a digital voltage detector with digital voltage display for armament circuit testing

ABSTRACT

A digital voltage detector system that is compatible with existing Armament Circuits Preload Test Sets is described. Adjustment of under and over voltage trip points is accommodated in accordance with conventional means. The digital voltage detector is compatible with all conventional Voltage Detector interface cables and adapters. Unlike the conventional voltage detector of existing Armament Circuits Preload Test Sets, over-voltage trips do not blow a fuse, eliminating the need to have replacement fuses or redundant conventional voltage detectors in an Armament Circuits Preload Test Set. Additionally, the digital voltage detector provides a digital voltage readout allowing the user to view the input voltage during a Presence of Voltage test. The digital voltage detector system facilitates timely and efficient execution of the Armament Circuits Preload Test series.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/136,656 filed on Jun. 10, 2008, the contents of which arehereby incorporated by reference in its entirety, and to which priorityis claimed herein.

BACKGROUND OF THE INVENTION

The present invention relates generally to voltage detectors and moreparticularly to a voltage detector suitable for use in an ArmamentCircuits Preload Test Set.

Armament Circuits Preload Test Sets, are used, for example, with air toair missiles, launchers, gravity and guided bombs, multi-ejector racks,and other munitions release systems on combat aircraft. Aircraft onwhich Armament Circuits Preload Test Sets are used include the F-15fighter, models A, B, C, D, and E. Armament Circuits Preload Test Setscomprise a voltage detector and interface adapters. The interfaceadapters provide electrical connection between the voltage detector andvarious connector types located on the aircraft. The conventionalvoltage detector performs at least four key test functions when used inan Armament Circuits Preload Test series. The voltage detector assessesPresence of Voltage, continuity in an Electroexplosive Device (EED), andStray Voltage. The voltage detector also performs an Adapter Test.

An EED conventionally consists of a conductor and a primary combustiblematerial. A variety of propulsion systems and ordnance use an electricalsignal to initiate combustion. This signal can be a dc current. Ohmicheating due to dc current flowing in the conductor can raise conductortemperature rapidly. Once a minimum ignition temperature of the primarycombustible material is reached, the primary material ignites, which inturn initiates combustion of a secondary material. Part of the ArmamentCircuits Preload Tests may include a continuity check in an FED. Thesame conventional voltage detector performs an ohmic Adapter Test andtwo voltage tests.

The Stray Voltage Test determines whether a circuit that is in anunenergized state is actually free of any voltage that could cause amalfunction in the tested circuit. For example, an FED must normally betested to ensure that the circuit is free of any stray voltages thatcould cause an improper triggering of the primary combustible material.

For the conventional voltage detector, an input voltage greater than0.120 VDC or less than −0.120 VDC causes the voltage detector to turn onthe indicator light. The conventional voltage detector comprises theattachment of a 3 ohm load resistance to the measurement circuit for theStray Voltage Test.

The Presence of Voltage test determines whether an input voltage between22.0 VDC and 47.0 VDC is present. In the conventional voltage detector,if an input voltage of less than 22.0 VDC is detected, then a test lightturns off. Alternatively, however, if the measured input voltage isgreater than 47.0 VDC, then a protection circuitry within theconventional voltage detector trips a protection fuse. Before theconventional voltage detector can make subsequent measurements, the fusemust be replaced. And the fuse is not readily accessible, requiring theremoval of screws for removal and replacement. Therefore, a technicianusing the conventional voltage detector would need to have spare fusesat hand and deal with the additional duties of repairing the voltagedetector before proceeding with an Armament Circuits Preload Test.Another alternative is to have multiple voltage detectors in eachArmament Circuits Preload Test Set.

The conventional voltage detector can also trip the indicator light fora voltage level less than 22.0 VDC and can also invoke the protectioncircuit for voltages greater than 47.0 VDC. That is, adjustments can bemade for measured-input voltage as low as 3.5 VDC to turn off theindicator light. Likewise, an over-voltage as high as 300 VDC can bemeasured before blowing the protective fuse.

External resistors are used to adjust the level for which the indicatorlight will turn off or for which the fuse will blow, under voltage andover voltage, respectively. The conventional analog voltage detector 100and internal resistors circuit 110 is shown in FIG. 1 a. The overvoltage protection circuit of the conventional voltage detector is notshown.

External resistors are used to vary the input voltage level which tripsunder voltage or over voltage. For an under voltage trip point greaterthan 22.0 VDC, an external resistor 126 is connected in series withTEST_IN+ 120 to create a voltage divider between the external resistorand the internal 300 ohm load 112, as shown in FIG. 1 b. Connection forTEST_IN+ measurement is moved to 121, in this configuration.

For an under voltage trip point of 3.5 VDC, the TRIP_ADJ pin 130 isconnected to TEST_IN+ 120 via connector 122, as shown in FIG. 1 c. Thisconfiguration raises the input voltage at sense input 142. For undervoltage trips between 3.5 and 22 VDC, the TRIP_ADJ pin 130 is connectedvia connector 122 to TEST_IN+ 120 and an external resistor 126 isconnected in series with TEST_IN+, moving the TEST_IN+ measuring pointto position 121, as shown in FIG. 1 d. Adjustments to raise the overvoltage trip point above 47.0 volts before triggering the overprotection circuit are not shown.

It would be desirable to have a voltage detector which is compatiblewith the Armament Circuits Preload Test Sets, which does not requirefuse replacement upon sensing of over-voltage.

SUMMARY OF THE INVENTION

The present invention addresses the issues presented above by providinga digital voltage detector system and method that are compatible withexisting Armament Circuits Preload Test Sets and that provide anaccurate digital voltage display. A digital voltage detector system andmethod, in accordance with the present invention can perform the fourrespective conventional Armament Circuits Preload Tests of Presence ofVoltage. Continuity in an EED, Stray Voltage, and Ohmic Adapter Test.

Another aspect of the present invention is to provide adjustment for thetrip point for the Presence of Voltage test using external resistors tolower the trip voltage.

Another aspect of the present invention is to provide adjustment for thetrip point for the Presence of Voltage test using external resistors toraise the Presence of Voltage trip voltage.

Another aspect of the present invention is a Digital Voltage Detectorwhich provides a digital readout allowing the user to view the inputvoltage during a Presence of Voltage test.

Another aspect of the present invention is to provide a fail indicatorlight in addition to a pass indicator light.

Another aspect of the present invention is to allow accurate measurementof high and low input voltages with a Digital Voltage Detector.

Another aspect of the present invention is to provide a Digital VoltageDetector which is compatible with all conventional Voltage Detectorinterface cables and adapters.

Another aspect of the present invention is to provide the technicianuser with input voltage measurement digital display, facilitatingproblem identification and troubleshooting.

Yet another aspect of the present invention is to enable reducedman-hours for completion of the Armament Circuits Preload Test series.

Yet another aspect of the present invention is to enable more timelyturn around of aircraft due at least in part to efficient execution ofthe Armament Circuits Preload Test series.

Yet another aspect of the present invention is to reduce equipmentredundancy in the conventional Armament Circuits Preload Test set.

Yet another aspect of the present invention is to reduce the need fordisposable fuses in an Armament Circuits Preload Test set.

Those skilled in the art will further appreciate the above-notedfeatures and advantages of the invention together with other importantaspects thereof upon reading the detailed description that follows inconjunction with the drawings.

BRIEF DESCRIPTION OF THE FIGURES

For more complete understanding of the features and advantages of thepresent invention, reference is now made to the detailed description ofthe invention along with the accompanying figures, wherein:

FIGS. 1 a-1 d show a schematic representation of a conventional voltagedetector for an Armament Circuits Preload Test Sets with externaladjustments to alter a trip point voltage;

FIG. 2 shows a digital voltage detector comprising an analog-to-digitalconverter and a microcontroller, replacing the analog comparator of theconventional voltage detector;

FIGS. 3 a-3 b illustrate a schematic representation of an exemplaryembodiment of a digital voltage detector in accordance with the presentinvention;

FIG. 4 illustrates a timing diagram in accordance with an exemplaryembodiment of the present invention; and

FIG. 5 illustrates a schematic representation of an exemplary embodimentof a digital voltage detector in accordance with the present inventionfor stray voltage measurements.

DETAILED DESCRIPTION OF THE INVENTION

The invention, as defined by the claims, may be better understood byreference to the following detailed description. The description ismeant to be read with reference to the figures contained herein. Thisdetailed description relates to examples of the claimed subject matterfor illustrative purposes, and is in no way meant to limit the scope ofthe invention. The specific aspects and embodiments discussed herein aremerely illustrative of ways to make and use the invention, and do notlimit the scope of the invention.

While an analog-to-digital converter and a microcontroller can besubstituted for the comparator 140 of the conventional voltage detector,100, an accurate digital voltage reading is not displayed for the user.FIG. 2 shows a digital voltage detector 200 comprising ananalog-to-digital converter 240 and a microcontroller 245, replacing theanalog comparator 140 of the conventional voltage detector 100. As inthe conventional voltage detector, the digital voltage detector 200 usesthe internal resistor circuit 110. The Digital Voltage Detector 200includes a digital display readout 270 in addition to PASS 250 and FAIL255 tights. A voltage between 22.0 and 47.0 VDC causes the DigitalVoltage Detector 200 to turn on the green PASS light 250. A voltagegreater than 47.0 VDC causes the Digital Voltage Detector 200 to turn onthe red FAIL light 255. A voltage less than 22.0 VDC causes the DigitalVoltage Detector 200 to turn both the PASS and FAIL lights 250, 255 off.

And, as in the conventional voltage detector 100, the trip point for thePresence of Voltage test can be adjusted using respective externalresistors in the presence or absence of a connector between the TRIP_ADJpin and TEST_IN+ as described in relation to FIGS. 1 a-d. These externalresistor and connector configurations yield accurate pass and failindicator light results. The pass indicator light 250 turns on for aTEST_IN+ that is within the desired voltage range, the fail indicatorlight 255, turns on for a TEST_IN+ that is above the desired voltagerange, and both lights turn off for a TEST_IN+ voltage which is belowthe range, under voltage. However, when an external resistor 226 isused, as the conventional user is accustomed, the display voltage 270 inthe digital voltage detector 200 is erroneous. The erroneous digitaldisplay is summarized in TABLE 1 with respect to values of the externalresistor 226 value in conjunction with the presence or absence ofconnector 222 between TRIP_ADJ pin 230 to TEST_IN+ 220, as shown in FIG.2.

Referring to TABLE 1 and FIG. 2, the Display Reading 270 is off of thetrue TEST_IN+ 221, input voltage, by the Error, in VDC. Use of anexternal resistor 226 and a connector 222, or the use of the connector222 alone, causes positive errors when displaying the input, TEST_IN+voltage. As in the conventional voltage detector, for an under voltagetrip point greater than 22.0 VDC, an external resistor 226 in theabsence of connector 222 is used. In the specific example of 381 ohmexternal resistor added in series with TEST_IN+ on the Digital VoltageDetector 200, the input under voltage trip point would change from 22.0VDC to 50.0 VDC. An applied voltage, Presence of Voltage of 50 VDC willcause the Digital Voltage Detector to turn on the PASS light 250correctly; however, the display 270 will show 22.0 VDC rather than theactual 50.0 VDC present at TEST_IN+ 121, Presence of Voltage.

TABLE 1 TEST_IN External TRIP_ADJ Display Input Range Resistorconnected? Reading Error 3.5 VDC s.c. Yes 22.0 VDC +18.5 VDC 5.0 VDC 128ohms Yes 22.0 VDC +17.0 VDC 10.0 VDC 557 ohms Yes 22.0 VDC +12.0 VDC15.0 VDC 986 ohms Yes 22.0 VDC +7.0 VDC 22.0 VDC s.c. No 22.0 VDC O VDC25.0 VDC 41 ohms No 22.0 VDC −3.0 VDC 35.0 VDC 177 ohms No 22.0 VDC−10.0 VDC 50.0 VDC 381 ohms No 22.0 VDC −28.0 VDC 100 VDC 1063 ohms No22.0 VDC −78.0 VDC 150 VDC 1745 ohms No 22.0 VDC −128 VDC 200 VDC 2427ohms No 22.0 VDC −178 VDC

Similarly, in the absence of connector 222, addition of an externalresistor 226, effectively lowers the under voltage trip voltage,however, the measured and displayed voltage 270 is constant at 22.0 VDC,proportionately less than the actual Presence of Voltage, TRIP_IN+. Thepass and fail tights still read correctly, however, the replacement ofthe voltage comparator 140 with the analog-to-digital converter 240 incombination with the conventional input resistor circuit, voltagedivider, yields 22.0 VDC at the display rather than the actual 3.5 VDCat TEST_IN+ 221.

Just substituting an ADC and microcontroller for the comparator isinsufficient as the conventional input voltage divider will consistentlyyield a 22 VDC display as measure of TEST_IN+ regardless of the actualTEST_IN+ range. This problem is solved and an accurate voltagemeasurement display for use by the technician is obtained in accordancewith the present invention as described below.

FIGS. 3 a-3 b illustrate schematic representations of an exemplaryembodiments of a digital voltage detector in accordance with the presentinvention. Turning to FIG. 3 a, the case in which the low voltage trippoint is lowered to 3.5 VDC by using a connector 322 from the TRIP_ADJpin 330 to TEST_IN+ 320 is shown. Rather than having the TRIP_ADJ pin330 change the input impedance to the voltage comparator 140, as shownin FIG. 1 c, an additional analog-to-digital converter 342 separatelymeasures the voltage on the TRIP_ADJ pin 330. As shown in FIG. 3 a, thevoltage at TRIP_ADJ is measured using an analog-to-digital converter342, which is separate from the analog-to-digital converter 340 used tomeasure the input voltage, TEST_IN+ 320. In this case, either a 3.5 VDCinput at TRIP_ADJ 330 or a 22 VDC input at TEST_IN+ 320 will cause thePASS light 355 to turn on, as dictated by microcontrollers 346 and 345,respectively. Microcontrollers are applicable in accordance with anexemplary embodiment, and any custom digital logic circuit whichanalyzes the output from the analog-to-digital converter can be used.The digital display 370, however, only shows the voltage input atTEST_IN+ 320.

FIG. 3 b shows the additional elements utilized for the case of a raisedPresence of Voltage under voltage trip point, wherein, an externalresistor 326 is placed in series with TEST_IN+. In addition, toaccurately report input voltage, an electronic switch 392 is placed inseries with the 300 ohm load resistor 381 on the TEST_IN+ signal 321.Switch 392 maybe a photoMOS relay, but it may also be a MOSFET or othertype of switch. Switch 392 is controlled by a Timing Control module 390in the software of the digital voltage detector in accordance with anexemplary embodiment of the present invention. The Timing Control 390module closes switch 392, engaging the 300 ohm resistor 382 to determineif the input voltage (TEST_IN+) is greater than the 22 VDC threshold orgreater than the 3.5 VDC threshold when connector 322 is in placeconnecting TRIP_ADJ pin 330. Periodically, the Timing Control Module 390briefly turns off the 300 ohm resistor 382, opens switch 392 andmeasures the input voltage at TEST_IN+ 321 when an external resistor 326and connector 322 are present. The measured and displayed voltage atTEST_IN+ is then the full input voltage without the 300 ohm loadimpedance 382. The Timing Control 390 directly measures the TEST_IN+voltage four times per second, measuring the input voltage for 4 ms 410,every 250 ms 420, as shown in the timing diagram in FIG. 4.

In the absence of an external resistor 326 or of a jumper 322, thecircuit has a threshold voltage of the nominal 22.0 VDC and the digitaldisplay gives a direct reading of the input voltage. When the externalresistor 326 is replaced by a wire or short circuit, the periodicopening and closing of the 300 ohm switch 392 will have minimal effecton the voltage measured at the analog-to-digital converter 440,affording a desired accurate display.

The conventional internal resistor circuit 110 includes a load resistor112 connected from TEST_IN+ 120 to TEST_IN− 125, a resistor 111 inseries with TRIP_ADJ 330, a two resistor voltage divider 113, 114 off ofTEST_IN+ 120, wherein resistor 111 is in parallel with resistor 113, asshown in FIG. 1.

In contrast, the internal resistor circuit 380, according to anexemplary embodiment of the present invention, includes a load resistor382 connected from TEST_IN+ 320 to via a switch 392 to TEST_IN− 325. Aresistor 381 is in series with TRIP_ADJ 330, while a two resistorvoltage divider 383, 384 is off of TEST_IN+ 320, and wherein resistor381 is in parallel with resistor 383, as shown in FIGS. 3 a and 3 b.Internal resistor circuit 380 also includes a putt down resistor 387.

The internal resistor circuit of the conventional voltage detector isdesigned to keep the analog-to-digital converter in the useable rangefor expected input voltages. In the conventional voltage detector, aninput impedance of approximately 3.385 Mega-ohms 113,114 is used for theinput sensing circuit 110, as shown in FIG. 1 a. The specific resistorvalues chosen cause the voltage at the negative input 142 of the analogcomparator 140 to equal a reference voltage of 2.5 VDC, when 22 VDC isapplied to the input circuit. When an external connector 122 is placedbetween the TEST_IN+ 120 and TRIP_ADJ 130 terminals, a tower impedance111 of 162 kilo-ohms is added in parallel to the circuit. This causesthe voltage at the negative input 142 to reach 2.5 VDC when an inputvoltage of only 3.5 VDC is applied.

In accordance with an exemplary embodiment of the present invention, theconventional input circuit 110 is replaced by an internal resistancecircuit 380 that includes two sets of measurement inputs and twoindependent analog to digital converters 340, 342. These differencesprovide improved consistency of input impedance at 2.1 Mega-ohmsregardless of the use of the input jumper 322.

Referring to FIG. 5, for the stray voltage test, in accordance with thepresent invention, another resistor circuit is applied between TEST_IN+and the analog-to-digital converter. In the stray voltage testconfiguration, a separate three ohm load resistance 501 is electricallyconnected to the TEST_IN+ connection, in the absence of the 300 ohm loadresistance employed in the presence of voltage tests. The control logicfor the stray voltage test includes a voltage threshold criteria 502that is set for voltages greater than 0.120 VDC or less than −0.120 VDC.The control logic also includes an overvoltage detector 503 that removesthe three ohm load resistor 501 from the input circuit via an electronicswitch 500. The switch may be a MOSFET relay or an electromechanicalrelay. Quickly removing the three ohm resistor 501 prevents damage tothe resistor and prevents fuses from being blown in the digital voltagedetector, in accordance with the present invention.

While specific alternatives to steps of the invention have beendescribed herein, additional alternatives not specifically disclosed butknown in the art are intended to fall within the scope of the invention.Thus, it is understood that other applications of the present inventionwill be apparent to those skilled in the art upon reading the describedembodiment and after consideration of the appended claims and drawing.

What is claimed is:
 1. A method of measuring a Presence of Voltage in anArmament Circuits Preload Test Series, the method comprising: using adigital voltage detector system; using a first digital converter with arespective microcontroller connected to a test input connection via afirst branch of an internal resistor circuit, and using a second analogto digital converter with a second respective microcontroller connectedto the test-adjustment lead via a second branch of the internal resistorcircuit; measuring a Presence of Voltage in an Armament Circuits PreloadTest Series; and displaying the measured voltage on a digital display.2. The method according to claim 1, further comprising: lowering anunder voltage trip point to a first voltage below a normal low voltagevalue by connecting a test-adjustment pin to a test input connection. 3.The method according the claim 2, further comprising: lowering an undervoltage trip point to a second voltage, which is greater than the firstvoltage and less than the normal voltage value, by connecting thetest-adjustment pin to a test input connection and connecting anexternal resistor in series to the test input connection.
 4. The methodaccording to claim 1, further comprising: raising an under voltage trippoint to a first voltage which is greater than the normal low voltagevalue by connecting an external resistor to a test input connection. 5.A method of measuring a Stray Voltage in an Armament Circuits PreloadTest Series, the method comprising: using a digital voltage detectorsystem; a first digital converter with a respective microcontrollerconnected to a test input connection via a first branch of an internalresistor circuit, and using a second analog to digital converter with asecond respective microcontroller connected to the test-adjustment leadvia a second branch of the internal resistor circuit; measuring a StrayVoltage in an Armament Circuits Preload Test Series; and displaying themeasured voltage on a digital display.
 6. The method according to claim5, further comprising: using a digital voltage detector system; using alow ohm load resistor connected to a positive test input connection;measuring a voltage at the positive test input connection; comparing anabsolute value of a measured voltage to nominal threshold voltage; andrendering a pass signal if the absolute value of the measured voltage isless than the nominal threshold voltage.
 7. The method according toclaim 6, wherein: using a digital voltage detector system; and quicklydisconnecting the low ohm resistor via a switch controlled by anover-voltage detector when a measure voltage exceeds an upper voltagelimit.